If you think you had an adversarial relationship with your siblings growing up, then you can at least be thankful (we hope) that they didn’t attempt to eat you. Young sand tiger sharks can’t make such a claim, however, for aggressive competition starts (and ends violently) in the womb for them.

Sand tiger sharks only give birth to one or two young, but they can carry as many as a dozen embryos. Why then do they not have a large brood of little sharks? It is because the strongest of the developing sharks in the womb eat any of the other sharks weak enough to succumb to them, ensuring the dominant sharks have more resources and a head start in life.

This behavior stems from the female sand tiger shark’s habit of mating with multiple males (rather than risking a physical confrontation with inferior but aggressive breeding partners). Everything sorts itself out in the womb, however brutal the sorting mechanism might be, when the offspring of the strongest male eats the offspring of the weaker ones.